Until now, the U.S. Supreme Court has been modestly deferential to Donald Trump’s executive overreach. Oral arguments in the case challenging the legality of the president’s tariffs suggest that this may be about to change.

The court’s three liberal justices appear sure to vote that Trump lacked the authority to impose the tariffs under the International Emergency Economic Powers Act (IEEPA). Chief Justice John Roberts, Justice Neil Gorsuch and Justice Amy Coney Barrett all sounded as though they were contemplating joining their liberal colleagues — each for reasons rooted in their individual versions of conservative jurisprudence. If at least two of them decided to join, as now seems possible, Trump will have to try and reimpose the tariffs based on a patchwork of other legal authorities, which might significantly constrain his ability to do so effectively.

The technical question before the court is whether the words “regulate … importation” in the IEEPA empower Trump to adopt essentially any tariffs he chooses once he has determined that an emergency exists under the statute. His best argument is that imposing tariffs is a means of regulating importation. A textualist reading of the statute would, under that interpretation, appear to support Trump’s power. What’s more, as Justice Brett Kavanaugh emphasized during oral arguments, former President Richard Nixon adopted a tariff under the authority of a predecessor statute to the IEEPA. That tariff was upheld by an appeals court — a fact that Congress knew when it enacted the IEEPA.

The arguments against Trump’s tariff power are varied — and as it happens, each of the conservatives who might vote against him has a different theory of why his actions are problematic. Roberts’s pet theory is the Major Questions Doctrine, known to Supreme Court nerds as MQD.

According to the MQD theory, which Roberts essentially invented in the 2022 case West Virginia v. EPA, when the executive branch takes an action with “major political or economic significance” that also goes well beyond previous exercises of executive power, the courts should reject that power unless Congress has expressly authorized it. The conservative majority of the court applied the doctrine to strike down both the Biden administration’s environmental regulations and its student-loan forgiveness program.

Supreme Court watchers, myself included, have speculated about whether the court would apply MQD in cases where a statute authorizes the president himself to act, not just an administrative agency. Roberts made it pretty clear that he thought the doctrine applied to Trump’s invocation of the IEEPA. “It seems that it might be directly applicable,” he noted. The IEEPA “had never before been used to justify tariffs” — evidence of the novelty of the claim. The claimed authority was sweeping, he continued, because “the justification is being used for a power to impose tariffs on any product from any country … in any amount for any length of time.” Roberts made no mention of any distinction between the statute giving authority to an agency and one giving authority directly to the president.

Urging Roberts on were the very same liberal justices who had dissented so sharply in the Biden-era cases in which Roberts introduced MQD. Justice Elena Kagan, who in a heated dissent had accused Roberts of “magically” inventing the doctrine, now argued (convincingly, I might add) that MQD should apply with particular force to the tariffs case because tariffs fall within Congress’s power to tax, and so can only be exercised by a president if expressly authorized by Congress. Justice Sonia Sotomayor, who also dissented in the Biden-era MQD cases, now objected to the Trump administration’s argument that the president’s foreign-affairs powers “or even an emergency can do away with the major questions doctrine.”

The liberals thus made it clear that if Roberts secures the single conservative vote he needs to decide the case against Trump on an MQD basis, they will join the opinion — a result that would enshrine the chief justice’s new doctrine as embraced by the entire court — albeit in very different political circumstances. You can be sure Roberts would love that.

Justice Neil Gorsuch, for his part, has for years sought to give teeth to the nondelegation doctrine — the idea that when Congress delegates authority to the president, it must provide limits on the extent to which that power can be exercised. Alluding to a power that the Constitution explicitly gives Congress, he asked Solicitor General D. John Sauer, “Could Congress delegate to the President the power to regulate commerce with foreign nations as he sees fit?” The question was meant to suggest that the answer was no.

When Sauer tried to insist that the tariffs were legitimate as an exercise of Trump’s executive power over foreign affairs, Gorsuch refused to take the bait, instead pressing Sauer about what principle limited Congress’s ability to delegate power. What would happen, he asked, if Congress were to decide “tomorrow, well, we’re tired of this legislating business. We’re just going to hand it all off to the President”?

Gorsuch is the justice most worried about nondelegation. Ordinarily, that’s a decidedly conservative position. Here, however, Gorsuch seemed to be considering the possibility that Congress could not lawfully tell the president that he could set tariffs in an unlimited way.

That left Barrett, who, as a follower of the late Justice Antonin Scalia, is deeply committed to interpreting statutes based on their text. (Barrett even has her own unique, textualist version of MQD — one that treats the doctrine not as a bright-line rule but as a “contextual” tool to help interpret the text.) Context, however, seemed to be undermined in the tariffs case. She asked the solicitor general, “Can you point to any other place in the [US] Code or any other time in history where that phrase together, ‘regulate ... importation,’ has been used to confer tariff-imposing authority?” Her point, which she repeated several times, was that the Trump administration’s interpretation of the words was not required by their plain meaning — at least in the context of tariff authority. Kagan made sure to back up Barrett’s point, too.

The takeaway is that the tariffs may actually fall because of the conservative justices’ sincere commitment to their own judicial philosophies. Back in 2019, when Trump’s IEEPA theory was first introduced, I wrote that “read very minutely, the IEEPA might not actually authorize the tariff. But it’s a very close call, and what little precedent there is arguably supports Trump’s use of the emergency powers to authorize the tariff.” Now it looks like the close call may go in favor of the separation of powers, not Trump. If so, the decision will represent a salutary turn to judicial enforcement of limits on presidential power.

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This column reflects the personal views of the author and does not necessarily reflect the opinion of the editorial board or Bloomberg LP and its owners.

Noah Feldman is a Bloomberg Opinion columnist. A professor of law at Harvard University, he is author, most recently, of “To Be a Jew Today: A New Guide to God, Israel, and the Jewish People."

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